More particularly, the invention relates to a seat element presenting, externally:
a first main face for supporting a user of the seat;
a second main face at a distance from the first main face and separated from said first main face by a certain thickness; and
four sides interconnecting the first and second main faces and defining the thickness of the seat element,
said seat element including padding supported by metal reinforcement extending at least along the four sides of the seat element, and covered by a flexible outer cover, which cover presents, firstly a central zone forming the first main face of the seat element and secondly, first, second, third, and fourth lateral panels forming the sides of the seat element, at least the first and second lateral panels which correspond to two opposite sides of the seat element having respective free edges in the vicinity of which there are formed buttonholes, said buttonholes being engaged on fastening members referred to as "main" fastening members, which are secured to the reinforcement and which are disposed in the vicinity of the second main face of the seat element, thereby tensioning the cover over the padding and the reinforcement.
The term "buttonhole" is used broadly to designate any orifice formed through the cover and capable of receiving a fastener member for fixing the cover.
An example of a seat of that type is disclosed in document FR-A-1 601 041.
In the seat disclosed in that document, the free edges of the side panels of the cover form hems that contain a reinforcing cable, such that the free edges are expensive to make.
Also, the fastener members of the seat disclosed in the above-mentioned document are constituted by triangular spikes of sharp shape that can not only injure operators required to handle the frame of the seat proper during manufacture of the seat, and in particular when installing the cover, but can also tend to spoil the cover, particularly if the cover is made of a material that does not have very great stiffness or strength.
This damage to the cover by the fastener means can lead rather quickly to the cover being stretched, and that must be avoided at all costs.
To avoid that drawback, it is generally necessary:
firstly to avoid the use of certain materials for seat cover manufacture, when such materials are not strong enough to withstand attack by the fastener members in the form of triangular spikes; and
secondly to use relatively stiff cables inserted in the above-mentioned hems to reinforce the free edges of the cover, or even to make use of rigid metal reinforcing rods.
The use of rigid rods or of cables gives rise firstly to a further increase in the cost of the cover, and secondly to the free edges of the cover being stiffened, which makes it considerably more difficult to put the cover into place during manufacture of the seat.